Clean the outside

Stainless with the grain, paint with soapy water

The manual and Weber UK's cleaning page.

1. Wait until the grill is cold.
2. Stainless (tables, panel, handle): a non-abrasive stainless cleaner for outdoor grills and a microfibre cloth, along the grain. No paper towels.
3. Painted, enamelled and plastic parts: warm soapy water and a soft cloth.
4. Rinse and dry thoroughly.
5. Near the sea or a pool, wash it more often and use stainless cleaner weekly: the manual makes this a warranty condition.
6. Never use a hose or a pressure washer: water can get into the ignition (Weber UK).